Two years ago, if you had asked me whether or not I recommended the canine influenza vaccine, I’d have told you, “probably not.” Even as recently as one year ago, I probably would have said the same thing, at least here in San Diego. But that’s the thing about medicine, especially when it comes to emerging diseases ... situations can change rapidly. Recommendations that made sense as recently as six months ago no longer hold. Such is the case with the current outbreak of canine influenza. Here’s what we know based on the latest information from the CDC, American Veterinary Medical Association and the veterinary schools who are helping to research the disease.

What is Canine Influenza?

Influenza is a family of viruses that affect a wide variety of species. It has two characteristics which really set it apart from other types of virus: one, it can mutate very rapidly (hence the need for a new flu vaccine every winter); and two, it often jumps species. Such is the case with canine influenza.

Until recently, the only strain we saw in dogs was H3N8, a mutation of equine influenza that’s been circulating in the United States since 2004. While a vaccine is available for H3N8, few veterinarians recommended it as the disease was very limited and most infected dogs recovered on their own.

All this changed in 2015, when H3N2 emerged on the scene. H3N2, thought to be a mutation of an avian influenza, arrived in Chicago with a group of dogs imported from Korea. This virus behaves very differently from H3N8, as the veterinary community soon discovered. It mutates very rapidly, meaning there are already different strains of the virus all around the country. Also, it is highly infectious, spreading to all corners of the US much more quickly than anyone had anticipated. As of now, H3N2 has been identified in 46 states.

What Does Canine Influenza Do to Dogs?

Canine influenza manifests in two forms. In the mild form of the disease, dogs experience a soft cough that lasts from 2-4 weeks. They may act lethargic, demonstrate a diminished appetite, have a low fever (102.5-104), exhibit sneezing, and maybe have some eye and nasal discharge. As you can see, these are fairly vague signs that show up with many sorts of canine disease processes, so many cases of canine influenza have probably gone unidentified.

In its rarer, more severe form, dogs can become very ill. They can run a high fever (104-106) and develop pneumonia, which can lead to life-threatening complications. The fatality rate for canine influenza is less than 10%.

Other species can be infected with H3N2: it’s been diagnosed in cats, ferrets and guinea pigs. In these species, it manifests like an upper respiratory infection and usually resolves on its own. Fortunately, H3N2 has not manifested in people according to the latest data from the CDC.

Which Dogs Are Most At-Risk?

In theory, all dogs are at-risk of H3N2. Virtually all dogs who are exposed to the virus become infected (i.e. have circulating virus in their systems); about 80% of those dogs show some clinical signs of disease. What makes this virus particularly nasty is that infected dogs shed tremendous amounts of the virus whether or not they are showing signs of disease; they can shed virus for more than three weeks! That means one dog, travelling across the country to dog shows or staying in boarding facilities, can infect hundreds of other dogs in a short period of time.

Dogs are at highest risk of exposure when they are in direct contact with other dogs. The virus only lives in the environment for 24 hours, so most infection occurs from contact with respiratory secretions like sneeze droplets. Dogs at boarding or daycare facilities, training classes, competitions, dog shows and shelters are at highest risk. Of these dogs, those who become the most ill are the very young, seniors and the immunosuppressed.

How is Canine Influenza Diagnosed and Treated?

Canine influenza can’t be definitively diagnosed based on history and examination because the symptoms are so vague. If your veterinarian suspects influenza, she may recommend specific blood or nasal swab tests which can isolate the canine influenza virus.

Like human influenza, the treatment consists of supportive care and treating the symptoms while the body fights off the virus. Fluid support and antibiotics for secondary infections are the mainstays of supportive care. Infected dogs should be quarantined from other dogs for at least 21 days.

Is There a Vaccine?

Two manufacturers make vaccines for H3N2. The vaccine schedule consists of two doses three weeks apart, with a yearly booster. If you are considering this vaccination for your dog, make sure you are getting the right one because a vaccine for H3N8 also exists.

If you’re not sure whether or not you should get your pet vaccinated, your veterinarian is always going to be the best source of information as they will be aware of whether the disease has been diagnosed in your area. You can also check out the Infectious Disease Risk Calculator from the Ohio State college of veterinary medicine, which asks you a series of questions and gives you a risk assessment based on the most current data (https://idrc.vet.ohio-state.edu).

The virulence of H3N2 took the veterinary community by surprise. Fortunately, public health surveillance exists specifically for this reason. The infectious disease community was able to identify and get the word out about H3N2 quickly, so veterinarians are able to better support the wonderful canines we are fortunate enough to treat. While the virus is scary, we know a lot more than we did even a few short months ago, including how to protect your pups. You can help by getting the word out about this virus, and encouraging those you know to visit the vet if there’s any concern H3N2 may be present.